Hacker News Reader

Comment by shriphani | Hacker News Reader

So we should be able to walk on the surface of a pool filled with ketchup?

I've seen this video of people walking on custard on brainiac: https://www.youtube.com/watch?v=Iz9KnPZWOgs

No, ketchup is shear-thinning, meaning it’s less solid when under stress.

I wonder if these properties are used in analog devices... I recently learned that ovens had thermal switches based on wax (and expansion under heat).

https://en.wikipedia.org/wiki/Wax_motor

If you've flown, you put your life in a wax motor's waxy hands: "Wax motors are used...to control fuel, hydraulic, and other oils critical to safe flight today in modern airplanes."

Melting / Solidifying wax is also the basis of old-school steam radiator thermostats.

And current-day car thermostats. If it fails, your engine overheats, and that's an expensive repair. If you ever see a high temp warning light on your car, you can take it out and test its functionality in a pot of hot water (or replace it for ~$20)

Also, was how the lunar rover handled cooling. Big block of wax used as a radiator. Well, not radiator exactly!

I don't think the LM used wax for thermal management, but the Lunar Roving Vehicle did, as a "thermal capacitor" [1]. That is, heat was stored in a block of wax while driving, and then radiated away between uses.

[1] https://en.wikipedia.org/wiki/Lunar_Roving_Vehicle#Wheels_an...

That’s what I said. Lunar rover.

https://en.wikipedia.org/wiki/Dilatant#Applications

I'd say that shear thickening fluids as used in traction control systems can be seen as an analog clutch.

ahh sadly the kevlar-fluid combo is already a thing.. i always thought it would be a fun thing to build

Even today the thermostatic valves you find on home heating radiators are actuated by wax.

The lock in a washing machine door works like that, which is why it takes two minutes to unlock.

I had assumed it was magnets!

magnetic wax

Yes, he needs to fill the pool with a dilatant fluid not a thixotropic fluid.

Just because it's non-Newtonian doesn't mean it's identical to oobleck. All it means is that it's not Newtonian.

Besides, you can run on water (or at least, some lizards can) at high enough speeds, though I'm not sure if water still behaves Newtonian in those situations.

For a human-sized object running on water, it's more about inertia - viscosity doesn't really come into it at that speed and scale. In other words, the Reynolds number is high in that situation.

Braniac is back? I miss that show

Unlikely - a spoon sinks in it.

Reply on news.ycombinator.com